Ethanol fermentation is a biological process in which organic material is converted by microorganisms to simpler compounds, such as sugars. These fermentable compounds are then fermented by microorganisms to produce ethanol and CO2. Ethanol has widespread application, including, as an industrial chemical, gasoline additive or straight liquid fuel. As a fuel or fuel additive, ethanol dramatically reduces air emissions while improving engine performance. As a renewable fuel, ethanol reduces national dependence on finite and largely foreign fossil fuel sources, while decreasing the net accumulation of carbon dioxide in the atmosphere.
Typically ethanol is produced by liquefying starch-containing material followed by sequential or simultaneous saccharification and fermentation. Liquefaction involves gelatinization of starch simultaneously with or followed by addition of alpha-amylase in order to degrade starch into dextrins. When producing ethanol the liquefied starch-containing material is saccharified. Saccharification is a step in which dextrins are converted to low molecular DP1-3 sugars that, e.g., can be converted by a yeast into ethanol.
The amount of ethanol produced from plant material can depend on the amount and availability of starch in the plant material, milling conditions, the type of yeast used, the fermentation conditions, and the like. Generally, plant varieties for use in ethanol production are selected based on the fermentability of the variety. In this field, although ethanol production has been greatly improved by new technologies, there are still challenges that need further investigations.